Tow trucks equipped with mechanisms for the recovery and transport of vehicles are well known in the vehicle towing industry. A wide variety of mechanisms have been developed to accomplish the towing of disabled or improperly parked vehicles with some success. One goal of a tow truck's lifting mechanism is to lift an end of a vehicle and enable its transport without damage to the vehicle. The simple, reliable and damage-free towing of a vehicle requires a mechanism engineered to accommodate a wide range of vehicle configurations.
A wheel lift is a category of vehicle lifting mechanisms that has proven to be effective for lifting and towing vehicles. The wheel is a point of potential attachment common to all wheeled vehicles. Wheel lift mechanisms typically attach to the wheels of a vehicle to be towed rather than the frame or undercarriage of the vehicle. The wheel is a desirable point of attachment and support for a vehicle because the vehicle's wheel suspension helps to smoothly transport the vehicle. The wheel is also a strong site for lifting, and similarly configured for most vehicles. Vehicles with contemporary styling often include air dams and ground effect packages that protrude down from the front of the vehicle. Lifting and towing such vehicles without damage to these undercarriage components creates difficulties. Wheel lift mechanisms attempt to overcome these difficulties by avoiding the fragile undercarriage components.
A conventional wheel lift mechanism that is successful utilizes an armature positioned beneath the vehicle and between a paired set of wheels that are mounted on the same axle. The wheels on both sides of the vehicle are supported from the armature positioned beneath the vehicle. This configuration is known as an internal wheel lift. U.S. Pat. No. 4,473,334 to Brown describes an outwardly directed U-shaped claw assembly that typifies the internal wheel lift.
The present invention is an improved internal wheel lift mechanism. A shortcoming in current tow truck mounted internal wheel lifting and towing mechanisms is the frequent damage incurred to undercarriages of vehicles during the lifting and towing process. Much of this damage is incurred during the attachment of the internal wheel lift to the vehicle. Punctured tires frequently result from improperly retaining a wheel, especially when hydraulic actuators as taught by Brown '334 are utilized to force the engagement of the wheels to be lifted. The Brown '334 patent also describes a pair of claws with prongs that are positioned to lift the wheels of a vehicle. The inventor of the present invention has discovered that if claws, tines, prongs or armatures are forced into the sidewall of a tire, damage to the tire frequently occurs, especially when the tire is tubeless as usually encountered, or the tire is already flat, as is often encountered. Therefore, a need exists for an internal wheel lift mechanism that retains the wheels of the towed vehicle without employing a locating and positioning means that potentially levers a mechanically powered claw, prong, boom or armature into the tire sidewall of the wheeled vehicle to be towed.
The operator of an internal wheel lift must retain the wheels of the vehicle to be towed with precision. Powered or hydraulic mechanisms often result in damage to the vehicle to be towed, simply as a result of the operator not being aware that there is damage occurring as the powered mechanism engages the vehicle. Also problem with existing internal wheel lift mechanisms is that they fail to allow the operator to directly and manually adjust the wheel lift mechanism to compensate for the variety of wheel diameters typically encountered, especially after the wheel lift mechanism has been initially positioned beneath the vehicle to be towed. Additionally, when the separated pairs of wheels are flat, as typically encountered after accidents and mishaps, hydraulic actuators acting in unison upon both sides of an apparatus are typically unable to compensate for imbalanced or asymmetric wheel configurations in which one of the vehicle's tires is missing of flat while the opposite tire is still intact and properly inflated.
Importantly, hydraulic or powered mechanisms significantly add to the expense and weight of the wheel lift mechanism. Specifically, FIG. 15 of the U.S. Pat. No. 4,473,334 to Brown shows the complex mechanism for expanding and retracting the wheel lift that includes hydraulic actuators mounted within telescoping support members. Hydraulic actuators are undesirable if they can be eliminated by simple manual mechanisms. This is attributable to the high expense of manufacturing, operating and maintaining hydraulic mechanisms, especially in the harsh environments in which many tow trucks must operate.
In another patent disclosure, the U.S. Pat. No. 4,573,857 to Porter, Sr. et al. shows a wheel supporting apparatus incorporated into a vehicle towing mechanism that includes a pair of L-shaped wheel engaging devices, each positioned at an end of a crossbar. The wheel engaging devices each have a rotating section and a fixed section. The rotating sections are hydraulically powered pivot to engage the wheels, after the crossbar is first positioned to place the fixed sections on the wheels of the towed vehicle.
Therefore, a need exists for an internal wheel lift mechanism that allows the operator to manually implement the positioning of the wheel lift mechanism to eliminate unnecessary powered actuators and additionally aid in compensating the wheel lift mechanism's configuration to accommodate a variety of wheel diameters.
Tow trucks are typically retro-fitted with lift mechanisms. Typically, the lift mechanism of a tow truck includes an extendable boom that can also be raised and lowered. The industry standard includes hydraulic actuation to achieve the required boom articulation. A transverse beam or crossbar mounted to the end of the boom is also a typical feature of tow trucks with wheel lifts. The transverse beam is typically pivotable and often hydraulically, to allow the operator to align the transverse beam with the wheels of a vehicle. The customizing of a lift mechanism is a difficult task, requiring expert technicians. To simplify the installation and retrofitting of a tow truck with the lift mechanism, the wheel lift mechanism must be compact and also accommodate the frame configuration of the tow truck which includes a boom and a transverse beam.
Prior wheel lift mechanisms fail to provide a configuration that is easily retrofitted to the standard lifting mechanism found in tow trucks. Therefore, a need exists for a lift mechanism that accommodates the boom and transverse bar configuration of a typical tow truck and is especially suited for a retro-fit installation.